Plasma volume support in cardiac surgery
Cardiac surgery involves major perturbations of normal physiology and organ perfusion including haemorrhage, an extracorporeal circuit, non-pulsatile blood flow, hypothermia and the resulting initiation of a systemic inflammatory response. Varying degrees of volume support are essential pre, during and post cardiopulmonary bypass (CPB), as avoiding hypovolaemia improves both organ perfusion and outcome. A target haematocrit determines whether or not blood is used; this review concentrates on available artificial solutions. The colloid versus crystalloid controversy smoulders on particularly regarding pump primes and practice differs between centres, with cost and concerns of the safety of various colloids remaining the major contentions. Whilst cost is an issue there is no convincing evidence linking adverse outcomes to modern colloid solutions. Using crystalloid solutions, an expansion of the interstitial space and reduced colloid osmotic pressure (COP) seem to be inevitable consequences of CPB. This may be important, because maintaining COP using colloid primes (often with hypertonic saline) has been associated with improved postoperative oxygenation and reduced ICU stay.
